1. Field of the Invention
The present invention relates to an antenna driving apparatus having a gear cover to protect gears for driving an antenna such as a parabola antenna.
2. Description of the Related Art
An antenna driving apparatus having a gear cover which covers a gear tooth portion of an antenna driving gear in order to protect the antenna driving gear from dust, rain water, etc. has been generally known as one type of antenna driving apparatus for a parabola antenna, etc. which is mounted on the ground.
This type of antenna driving apparatus is disclosed in Japanese Utility Model Application Laid-open Publication No. Sho-57-46309 entitled "ANTENNA APPARATUS HAVING GEAR PROTECTION COVER", and this apparatus is constructed as shown in FIGS. 1 to 3.
The antenna driving apparatus as disclosed in the above publication will be described with reference to FIGS. 1 to 3. In the figures, reference numeral 1 represents an antenna driving apparatus which includes a driving force transmitting gear 2, an antenna driving gear 3 and a gear cover 4.
The driving force transmitting gear 2 is rotated by a driving source 5 such as a motor, and it is mounted on an antenna support table 6. The antenna driving gear 3 is provided with a tooth portion 3a which is formed on the periphery thereof and pivotally rotated around a center shaft (elevation axis) 7 by the driving force transmitting gear 2. The tooth portion 3a is provided substantially 90 degrees around the center shaft 7 in the peripheral direction thereof. The antenna driving gear 3 is mounted on the antenna support table 6. A parabola antenna (antenna main reflection mirror) 8 is rotated by the above units. Further, a guide rail 9 is mounted on each side surface of the antenna driving gear 3 so as to extend along the peripheral or circumferential direction.
The gear cover 4 comprises a plurality of gear cover elements 4a (4a1, 4a2, . . . , 4an), and gear cover elements 4a1, 4a1 at both end portions relative to the peripheral direction are fixed to the side surface of the antenna driving gear 3 and the antenna support table 6, respectively. Each gear cover element 4a (4a1, 4a2, . . . , 4an) which covers the gear tooth portion 3a of the antenna driving gear 3 is mounted on the guide rail 9 through a shoe 10 so that the gear cover 4 is freely expanded and contracted in the peripheral direction.
Each cover element 4a1, 4a2, . . . , 4an of the gear cover 4 is made of metal and has a box shape, and the tooth portion 3a of the antenna driving gear 3 faces the inside of each cover element. Each cover element 4a1, 4a2, . . . is formed with an inner space therein so that a cover element at an antenna driving gear side of the adjacent cover elements can accommodate an antenna support table side of a cover element therein. Accordingly, the cover elements 4a1, 4a2, . . . , 4an are designed so that the cover element 4an at the terminal end has the largest inner space and the cover element 4a1 at the starting end has the smallest inner space, whereby the gear cover 4 can be expanded and contracted by changing a relationship in the circumferential position between the neighboring cover elements in accordance with the rotation of the antenna driving gear 3. FIG. 1 shows an expanded state of the gear cover 4, while FIGS. 2 and 3 show a contracted state of the gear cover 4.
In the above conventional antenna driving apparatus, the cover element at the antenna driving gear side of the adjacent cover elements 4a1, 4a2, . . . , 4an is designed in such a shape that it can accommodate the cover element at the antenna support table side of the adjacent cover elements, and thus the respective cover elements 4a1, 4a2, . . . , 4an must be designed to be different sizes. As a result, the respective cover elements 4a1, 4a2, . . . , 4an are designed to be different shapes or sizes, and this makes it cumbersome to manufacture the gear cover 4.
Further, since the respective cover elements 4a1, 4a2, . . . , 4an are designed so that the rear cover element (antenna driving gear side cover element) can accommodate the adjacent front cover element (antenna support table side of the cover element) therein, the cover elements are gradually larger in the order from the cover element 4a1 at the start end to the cover element 4an at the terminal end, and thus the overall gear cover size is increased.
Still further, since each cover element 4a1, 4a2, . . . , 4an is formed into a box shape, it is necessary to detach the gear cover 4 from the antenna driving gear 3 for cleaning and inspection, and this makes the cleaning and inspection of the gear cover 4 cumbersome.